Biochemical Changes Involved in the Decomposition of Hemp Bark by Pure Cultures of Fungi

Abstract

Fungi are believed to be responsible in great measure for the field retting of hemp in Iowa. Species of various genera commonly found on retting hemp were described by Fuller and Norman (1944). In the early fall of 1944, during a warm and unusually humid period, Trichothecium roseum, either alone or, not infre-quently, associated with Cephalosporium, was observed to be dominant on local areas of some hemp stalks. The ubiquitous species of retting fungi, previously described, seemed to be absent from these local areas, though present on other parts of the stalks. It was further noted that the fiber in these local areas be-came exceptionally weak or almost completely deteriorated, in contrast to that of the remainder of the stalk where retting appeared normal. In certain Iowa counties a considerable amount of the hemp was damaged in this manner. It therefore appeared to be of interest to investigate the relative activity of these organisms with other pure cultures of fungi isolated from retting hemp. The biochemical changes brought about in the fiber-containing tissues of the hemp stalk under optimum conditions have therefore been determined. It was not considered likely that fiber deterioration is brought about only by particular fungi, but that certain organisms are relatively more active than others in the same period of time. Overretting readily occurs if hemp is left in the field too long, and if adequate moisture is present, regardless of what group of organisms predominates. In studies of flax retting, Jensen (1941) found T. roseum to be the dominant fungus on deteriorated dew-retted flax straw and Stachybotrys to be particularly destructive to the fiber in pure culture. Ruschmann and Bartram (1940) stated that Alternaria tenuis is active in flax retting as well as in subsequent fiber destruction. Ruschmann (1923), in addition, considered Clado-sporium herbarum (syn. Hormodendrum herbarum) to have a tendency to cause damage to flax fiber. EXPERIMENTAL Source and treatment of material. Green, unretted hemp from Grundy Center, cut September 25, 1944, was decorticated in a smali Johansen decorticator. The isolated bark3 was cut into pieces a to 1 inch in length, weighed into 15 g lots, and placed in pint milk bottles. The bottles of hemp were sterilized for 10 minutes at 15 pounds' pressure in an autoclave for two periods 24 hours apart. Additions of 15 ml of water were made to the bark prior to sterilization. Organisms. Species of Alternaria, Hormodendrum, Fusarium, Phoma, Cephalo-sporium, and Trichothecium roseum were isolated from field-retting hemp and cultured on Czapek's agar in 8-oz bottles. Decomposition technique. Each milk bottle of hemp received 15 ml of a heavy suspension of spores of the desired organism. The added moisture was sufficient to saturate the hemp bark but did not allow appreciable amounts of free water to collect. Decomposition at 2S C was allowed to continue in one series for 5 days, in another for 10 days, and in a third for 20 days. Sterilized, but uninocu-lated, samples were prepared and allowed to stand for equal periods as reference material. The total loss in weight was calculated at the end of the period after drying the samples at 40C overnight, weighing, and sampling for moisture. The material for chemical analysis was prepared by grinding in a Christy and Norrs mill. Analytical methods. (1) Water-soluble constituents. The quantity of hot water-soluble constituents was determined by extracting about one gram of the residue with hot water at 75 C for one hour. (2) Cellulose. The cellulose was determined by the method suggested by Norman and Jenkins (1933). (3) Furfuraldehyde yields. Furfural was determined by the official A.O.A.C. method. (4) Urone. The urone units were determined by decarboxylation of uromc carboxyl groups on boiling with 12 per cent HCl (Bartholomew and